Some of known strain detectors include a strain gauge configured to detect strain caused on a strain-causing portion as electric signals, and an electrode pad connected to the strain gauge through an electrode wiring.
A semiconductor pressure sensor as a typical example of the strain detector includes: a printed board also serving as a stem; a pressure-sensitive diaphragm chip mounted on the printed board, the pressure-sensitive diaphragm chip including a silicon wafer diaphragm and strain gauge resistors provided on the diaphragm in a dispersed manner; and a wire connecting a surface electrode on the chip and the printed board (Patent Literature 1; JP 3099584 B).
In the typical example disclosed in Patent Literature 1, silicone gel is coated on the surface of the chip in order to protect the pressure-sensitive diaphragm chip from being corroded due to moisture and the like.
When the thickness of the silicone gel is thick at the center of the pressure-sensitive diaphragm chip and is thin at a periphery of the pressure-sensitive diaphragm chip in the typical semiconductor pressure sensor, a stress caused due to temperature change is not evenly applied on the chip, which adversely affects pressure detection sensitivity.
Accordingly, the silicone gel is filled in a case in which the pressure-sensitive diaphragm chip and a wire are housed, and subsequently the silicone gel is sucked out of the case so that the silicone gel is applied evenly all over the surfaces of the pressure-sensitive diaphragm chip and the wire.
In the typical example disclosed in Patent Literature 1, since the silicone gel is filled in the case in which the pressure-sensitive diaphragm chip and the wire are housed, much amount of the silicone gel have to be used. In addition, since a device for filling the case with the silicone gel is required, a size of equipment becomes large. In addition, since the silicone gel is filled after a surface electrode on the chip and the printed board are connected via the wire, the presence of the wire may sometimes hinders the filling process of the silicone gel, thereby complicating the manufacturing process of the sensor.